If you use (K)Ubuntu linux 7.10, Gutsy Gibbon, avoid using the new release of Opera web browser made especially for it. Based on my experiences, the combination poses a risk to your data and hardware.
One of the first things I did after installing Kubuntu on my system was to install Opera 9.24 - the version built for the previous release of Ubuntu, Feisty Fawn, because no Gutsy-specific version had been released yet. It turned out that this was one of the bigger disappointments in my use of Ubuntu, because it was terribly crash-prone. I left it out of my previous reports because it was an inappropriate release. But now that there is a Gutsy build, I'm afraid that it's much, much worse. Running that release of Opera, my entire system would freeze up after about 15 minutes of use, necessitating a hardware reset with the Reset button. At first I blamed the hardware until I realised that every time this happened, Opera had window focus. I avoided it for a while and the system stopped freezing up.
This isn't exacly a scientific way to determine the cause of a problem, and I'm trying very hard not to lay all of the blame at Opera Software's feet. But my experiences over a number of years have been that Opera has had widely varying stability on linux, ranging from very bad (Opera 6 on SuSE 8 was a particularly nightmarish release IIRC) to OK (Opera 9.* on SuSE linux 10.0 was stable enough), and its poor performance on Mac OS X made me abandon it on the iBook in favour of Safari. If not Opera on its own, then the combination of this particular release/build with this particular flavor/configuration of linux causes system freezes of the kind that are bad for my system. So rather than investigate further, I've switched all my web browsing over to Firefox and my email to Thunderbird.
I've never been fond of Mozilla Firefox, but I use it at work, and have found that it's improved quite a bit. Opera may be more innovative and comfortable, but Firefox is now very close, and any Opera feature that I use is available in a number of competing versions. I'll get used to this.
Anyway. I just thought I'd warn you. Your mileage may vary.